Satellite radioterminal communications systems and methods are widely used for radioterminal communications. Satellite radioterminal communications systems and methods generally employ at least one space-based component, such as one or more satellites that is/are configured to wirelessly communicate with a plurality of satellite radioterminals.
A satellite radioterminal communications system or method may utilize a single antenna pattern (i.e., a global beam) to cover an entire area served by the system. Alternatively, or in combination with the above, in cellular satellite radioterminal communications systems and methods, multiple antenna patterns (i.e., beams or cells) are provided, each of which can serve a substantially distinct geographical area in an overall service region, to collectively serve an overall satellite footprint. Thus, a cellular architecture similar to that used in conventional terrestrial cellular radioterminal systems and methods can be implemented in cellular satellite-based systems and methods. The satellite typically communicates with radioterminals over a bidirectional communications pathway, with radioterminal communications signals being communicated from the satellite to the radioterminal over a service downlink (forward-link), and from the radioterminal to the satellite over a service uplink (return-link).
The overall design and operation of cellular satellite radioterminal systems and methods are well known to those having skill in the art, and need not be described further herein. Moreover, as used herein, the term “radioterminal” includes cellular and/or satellite radioterminals with or without a multi-line display; Personal Communications System (PCS) terminals that may combine a radioterminal with data processing, facsimile and/or data communications capabilities; Personal Digital Assistants (PDA) that can include a radio frequency transceiver and/or a pager, Internet and/or Intranet access, Web browser, organizer, calendar and/or a global positioning system (GPS) receiver; and/or conventional laptop and/or palmtop computers or other appliances, which include a radio frequency transceiver. As used herein, the term “radioterminal” also includes any other radiating user device/equipment/source that may have time-varying or fixed geographic coordinates, and may be portable, transportable, installed in a vehicle (aeronautical, maritime, or land-based), or situated and/or configured to operate locally and/or in a distributed fashion at any other location(s) on earth and/or in space. A radioterminal also may be referred to herein as a “radiotelephone,” a “mobile terminal,” a “mobile user device,” a “user device” or simply as a “terminal.” Furthermore, as used herein, the term “space-based component” or “space-based system” includes one or more satellites at any orbit (geostationary, substantially geostationary, medium earth orbit, low earth orbit, etc.) and/or one or more other objects and/or platforms (e. g., airplanes, balloons, unmanned vehicles, space crafts, missiles, etc.) that has/have a trajectory above the earth at any altitude.
Cellular satellite communications systems and methods may deploy hundreds of antenna patterns, each of which may correspond to one or more spot beams or cells, over a satellite footprint corresponding to a service area. It will be understood that large numbers of cells may be generally desirable, since a frequency reuse and a capacity of a cellular satellite communications system or method may both increase in direct proportion to the number of cells. Moreover, for a given satellite footprint or service area, increasing the number of cells may also provide a higher gain per cell, which can increase a link robustness and improve a quality of service.
The uplink and/or downlink communications between wireless terminals and a space-based component (e.g., a satellite) may utilize one or more air interfaces, including proprietary air interfaces and/or conventional terrestrial cellular/PCS interfaces, such as, for example, Time Division Multiplexed (TDM) and/or Time Division Multiple Access (TDMA), Code Division Multiplexed (CDM) and/or Code Division Multiple Access (CDMA), Frequency Division Multiplexed (FDM) and/or Frequency Division Multiple Access (FDMA), Orthogonal Frequency Division Multiplexed (OFDM) and/or Orthogonal Frequency Division Multiple Access (OFDMA) air interfaces and/or various adaptations and/or combinations thereof. A single air interface may be used throughout the cellular satellite system. Alternatively, multiple air interfaces may be used for the satellite communications. See, for example, U.S. Pat. No. 6,052,560, issued Apr. 18, 2000, entitled Satellite System Utilizing a Plurality of Air Interface Standards and Method Employing the Same, by the present inventor Karabinis. In general, regardless of the air interface or interfaces that are used, each satellite cell generally uses at least one carrier and/or channel to provide signaling and/or communications service in a specified direction (forward or return). Thus, each satellite cell (satellite beam or satellite antenna pattern) must generally be configured to provide at least one return service link (carrier and/or channel) and at least one forward service link (carrier and/or channel) to serve at least one radioterminal.
As is well known to those having skill in the art, a terrestrial network can enhance an availability, efficiency and/or economic viability of a satellite radioterminal system by terrestrially using/reusing at least some of the frequencies that are allocated to the cellular satellite radioterminal system. In particular, it is known that it may be difficult for the cellular satellite radioterminal system to reliably serve densely populated areas, because satellite signals may be blocked by high-rise structures and/or may not penetrate into buildings. As a result, satellite frequencies may be underutilized or unutilized in such areas. The use of terrestrial transmission and/or retransmission of all or some of the satellite band frequencies can reduce or eliminate this problem.
Moreover, a capacity of an overall hybrid system, comprising space-based (e.g., satellite) and terrestrial communications capability, can be increased significantly by the introduction of terrestrial transmission/retransmission, since terrestrial frequency use/reuse can be much denser than that of a space-based-only system. In fact, capacity can be enhanced where it may be mostly needed, i.e., in and/or proximate to densely populated urban, industrial, and/or commercial areas. As a result, the overall hybrid system can become much more economically viable, as it may be able to serve a much larger subscriber base. Finally, radioterminals for a hybrid system, wherein space-based and terrestrial communications are provided within a common frequency band (e.g., within a frequency band authorized for use by a space-based component of the hybrid system) using substantially the same air interface for both terrestrial and space-based communications can be more cost effective and/or aesthetically appealing. Exemplary conventional dual band and dual mode satellite and terrestrial radiotelephone systems include Thuraya, Iridium and Globalstar.
U.S. Pat. No. 6,684,057 issued Jan. 27, 2004, to the present inventor Karabinis, and entitled Systems and Methods for Terrestrial Reuse of Cellular Satellite Frequency Spectrum, the disclosure of which is hereby incorporated herein by reference in its entirety as if set forth fully herein, describes that a satellite radioterminal frequency can be reused terrestrially by an ancillary terrestrial network even within the same satellite cell, using interference cancellation techniques. In particular, the satellite radioterminal system according to some embodiments of U.S. Pat. No. 6,684,057 includes a space-based component that is configured to receive wireless communications from a first radioterminal in a satellite footprint over a satellite radioterminal frequency band, and an ancillary terrestrial network that is configured to receive wireless communications from a second radioterminal in the satellite footprint over the satellite radioterminal frequency band. The space-based component also receives the wireless communications from the second radioterminal in the satellite footprint over the satellite radioterminal frequency band as interference, along with the wireless communications that are received from the first radioterminal in the satellite footprint over the satellite radioterminal frequency band. An interference reducer is configured to reduce the interference from the wireless communications that are received by the space-based component from the first radioterminal in the satellite footprint over the satellite radioterminal frequency band, using the wireless communications that are received by the ancillary terrestrial network from the second radioterminal in the satellite footprint over the satellite radioterminal frequency band.
United States Patent Application Publication No. 2003/0054761 A1, published Mar. 20, 2003 to the present inventor Karabinis and entitled Spatial Guardbands for Terrestrial Reuse of Satellite Frequencies, the disclosure of which is hereby incorporated herein by reference in its entirety as if set forth fully herein, describes satellite radioterminal systems that include a space-based component that is configured to provide wireless radioterminal communications in a satellite footprint over a satellite radioterminal frequency band. The satellite footprint is divided into a plurality of satellite cells, in which satellite radioterminal frequencies of the satellite radioterminal frequency band are spatially reused. An ancillary terrestrial network is configured to terrestrially reuse at least one of the radioterminal frequencies that is used in a satellite cell in the satellite footprint, outside the cell and in some embodiments separated therefrom by a spatial guardband. The spatial guardband may be sufficiently large to reduce or prevent interference between the at least one of the satellite radioterminal frequencies that is used in the satellite cell in the satellite footprint, and the at least one of the satellite radioterminal frequencies that is terrestrially reused outside the satellite cell and separated therefrom by the spatial guardband. The spatial guardband may be about half a radius of a satellite cell in width.
Various beam forming techniques may be used to enhance performance in satellite communications systems. United States Patent Application Publication No. US 2003/0054815 A1, published Mar. 20, 2003 to the present inventor Karabinis, and entitled Methods and Systems for Modifying Satellite Antenna Cell Patterns in Response to Terrestrial Reuse of Satellite Frequencies, the disclosure of which is hereby incorporated herein by reference in its entirety as if set forth fully herein, describes that space-based wireless radioterminal communications are provided in a satellite footprint over a satellite radioterminal frequency band. The satellite footprint is divided into satellite cells in which satellite radioterminal frequencies of the satellite radioterminal frequency band are spatially reused. At least one of the satellite radioterminal frequencies that is assigned to a given satellite cell in the satellite footprint is terrestrially reused outside the given satellite cell. A radiation pattern of at least the given satellite cell is modified to reduce interference with the at least one of the satellite radioterminal frequencies that is terrestrially reused outside the given satellite cell.
A U.S. patent application Ser. No. 11/324,711, entitled Adaptive Beam Forming with Multi-User Detection and Interference Reduction in Satellite Communications Systems and Methods, filed Jan. 3, 2006, the disclosure of which is hereby incorporated herein by reference in its entirety as if set forth fully herein, describes receiving multiple access signals at a space-based component from a plurality of terminals in a satellite footprint over a satellite frequency band. Multiple access signals may be received using an antenna including a plurality of antenna feed elements that may be configured to provide antenna patterns that differ in spatial orientations therebetween, wherein at least some of the antenna feed elements may also be configured to receive electromagnetic energy over at least two different polarization orientations.
The above description has focused on communications between a satellite and wireless terminals. However, cellular satellite communications systems and methods also generally employ a bidirectional feeder link for communications between a satellite gateway and the satellite. The bidirectional feeder link includes a forward feeder link from the gateway to the satellite and a return feeder link from the satellite to the gateway. The forward feeder link and the return feeder link each use one or more feeder link carriers and/or channels of a feeder link band of frequencies.
United States Patent Application Publication No. US 2005/028801 A1, published Dec. 29, 2005, to Santanu Dutta and entitled Methods of Ground Based Beamforming and On-Board Frequency Translation and Related Systems, the disclosure of which is hereby incorporated herein by reference in its entirety as if set forth fully herein, describes that a feeder link may be provided between a satellite and a satellite gateway over a feeder link frequency band for communication of information between the satellite gateway and the satellite. A service link may be provided between the satellite and at least one radioterminal in a coverage area of the satellite over a service link frequency band, and the feeder link and service link frequency bands may be different. In addition, a frequency segment of the feeder link may be linearly translated from the feeder link frequency band to the service link frequency band to provide a frequency segment of the service link. The frequency segment of the service link may provide content for the at least one radioterminal and/or for a plurality of radioterminals in the coverage area.
United States Patent Application Publication No. US 2005/0260947 A1, published Nov. 24, 2005 to the present inventor Karabinis, entitled Satellite Communications Systems and Methods Using Radiotelephone Location-Based Beamforming, the disclosure of which is hereby incorporated herein by reference in its entirety as if set forth fully herein, describes that a return-link processor for use in a satellite communications system may include a selector that is configured to select a subset of a plurality of spatially diverse satellite signals, i.e., signals having diverse spatial content, based upon a location of a radioterminal. The return-link processor may further include a signal processor that is configured to detect a return-link transmission from the radioterminal responsive to the selected subset of the spatially diverse satellite signals.